- All patients who have confirmed CDAD, confirmed by testing at UPMC's clinical microbiology lab in March 1, 2001- December 31, 2005 for C. difficile by stool toxin test with subsequent positive culture for the organism from inpatients/outpatients at UPMC Presbyterian-Montefiore, from WPIC inpatient units, from ER visits at the Presbyterian University Hospital emergency department, and from clinics closely affiliated with UPMC Presbyterian (medical and surgical clinics in Falk Clinic, the 9 South Montefiore internal medicine clinic, the geriatrics clinic in Montefiore, and the digestive disorders center (GI clinic on 3rd floor of PUH).